Even though there is water in the pump housing, I err on the side of not starting the boat out of the water unless it is hooked up to a water source. If you are worried about your battery's state, just turn on the blower. If it sounds weak, you may want to check the battery. If it fires up loud as ever, you're probably good to go. You should be running the blower anyway, right?

Also, if you have a fair amount of down time between uses, a battery cut off switch is a good investment. My boats have always managed to have one sort of phantom draw or another that will drain the battery over time. The switch is cheaper and easier for me than chasing the source of the draw.

Also, we have a battery powered jump starter that we keep charged up and take on the boat with us. It isn't huge and is good insurance.